1. Field of the Invention
This invention relates to paging receivers, and more particularly, to a paging receiver for receiving information including analog voice messages, digitizing the analog voice messages and storing the voice messages in a memory for playback.
2. Background of the Invention
Communications systems in general and paging systems in particular using transmitted call signals have attained widespread use for calling selected receivers to transmit information from a base station transmitter to the receivers. Modern paging systems and paging receivers in particular have achieved multifunction capabilities through the use of microcomputers which allow the paging receiver to respond to information having various combinations of tone, tone and voice, or data messages. This information is transmitted using any number of paging coding schemes and message formats.
In the operation of such paging receivers, important factors involved in their successful operation is the portability of the receiver, the limited energy available for the receiver, the limited availability of the radio spectrum, the fast response time required in today's active Society, and the number of paging receivers included in the paging system. In such paging receivers, in order that the drain on the battery may be minimized, the paging receiver is systematically turned off and turned on to maximize the length of time energy is available from the battery (battery saving). The limited energy in which the paging receiver must operate constrains the type of electronic circuitry available for a paging receiver.
A typical voice type paging system uses analog voice channels for the transmission and reception of voice messages. While certain types of paging systems use binary signalling formats, transmission in an analog form remains the most common technique for voice signals. Prior art paging receivers that receive analog representation of voice signals are limited in several features that would be highly desirable. These include the ability to store a voice message in a reasonable size memory for recall at a later time and use of digital modulation techniques to store and reconstruct voice messages in the paging receiver. Digital processing of voice messages is, in general, qualitatively superior to analog processing. This is a result of the fact that once the voice message is in a digitally-represented form, it is not subject to the type of signal degradation that occurs in analog processing. Thus, it is beneficial to represent the voice message in digital form rather than as a voltage subject to the type of distortion inherent in analog processing techniques.
Another problem with prior art analog voice paging receivers is the ability to store a plurality of voice messages and selectively recall a voice message. Prior art analog voice paging receivers have typically stored the voice information on conventional analog magnetic tapes (e.g. U.S. Pat. No. 4,356,519). While such voice type paging receivers are available, they are typically commercially inoperative. Some of the reasons are the cost of the electronic components, the low battery life from the high drain of current required by the tape mechanism, and the difficulty in operating in a battery saving environment. Additionally, if a sequence of messages is stored on the tape, the recall of a single message is hampered by the inability of the analog magnetic tape to randomly select a single message.